Transformer



July 4, 1933.

A. J. WILLIAMS, JR

TRANSFORMER Filed Feb. 2, 1952 [NV EN TOR.

ATTORNEY.

Patented July 4, 1933 7 ALBERT I. WILLIAMS, TR, Oil PHILADELPHIA, PENNSYLVANIA,.ASSIGNOR TO LEEDS & NORTHR'UP COMPANY, PENNSYLVANIA OI PHILADELPHIA, PENNSYLVANIA, A CORPORATION 01" TRANSFORMER Application filed February 2,1932. Serial No. 590,331.

' operation of the circuit.

In accordance with the invention, in a shielded type of transformer, freedom from interference is obtained by the combination of balanced core structure and shielding means symmetrically disposed about given planes of symmetry of the core structure; more specifically, the transformer windings are arranged symmetrically on a symmetrical core, and one or more magnetic shields are disposed around the core and ,windings symmetrically with respect to two imaginary planes, one of which is midway between and parallel to the axes of the windings, and the other of which passes through and midway between the ends of the windings, said planes being perpendicular to each other and to an ima 'nary plane passing through the axes of t e wlndings.

Further in accordance with the invention, the core does not have to be given a special shape, and therefore the common rectangular sha ed core, or cores of other desired configurations, may be used. The windings or coils do not have to 'be wound in place by hand or by special machinery, but may be separately wound on bobbins and then placed over the legs of the core. Also, the shields do not have to assume a particular configuration to conform to the core, but may have any desired form as long as they are symmetrical with respect to certain planes hereinafter described. Transformers in which interference is reduced to a negli 'ble degree may therefore be made in any esired shape and without special machinery, and by quantity production methods with consequent reduced cost of manufacture.

The invention further resides in the fea-' tures of construction and combination hereinafter disclosed and claimed.

For an understanding of the invention, and some of the forms it may take, reference is had to the accompanying drawing, in which: I

Fig. 1 is a view in front elevation, partly in section, of a transformer constructed in accordance with the invention.

Fig. 1a is a perspective view of the transformer core and windings, the arrows indieating a given external disturbing field.

Fig. 2 is a side elevational view, partly in section of the transformer, taken along the line 22 of Fig. 1, and

Fig. 3 shows the transformer core and windings of Fig. 1 enclosed in a plurality of shields.

In various circuits and arrangements in which feeble electric currents or potentials are produced, for example, by a thermocouple, and in which it is desired to actuate structure, such as a recorder, control apparatus, or the like, in response thereto, it is often desirable or necessary to amplify the feeble currents, as by a thermionic amplifier. Due to the Very small magnitudes of the currents or potentials produced by the thermocouple, which may be of the order of 1 microvolt, the corresponding amplified currents passing through the trans-. formers in the input and output circuits of the tubes of the amplifier are also small. The transformers are subject to disturbing magnetic fields and the resultant effects of these fields in the windings of the transformers may be comparable with the transformer currents before or after amplification, so that super-position. of the disturbing effects thereon will introduce substantial error in the measuring or control system. A system of the foregoing type, and generically representing the field of application of my transformers, is disclosed in my copending application Serial No. 634,425, filed September 22, 1932, a continuation in part of my application Serial No. 569,126, filed October 15, 1931; and the present invention is particularly applicable to the transformers in the input and output circuits of one or more of the amplifier stages of such a system to avoid the disturbing effects upon the system of stray electric or magnetic fields which would otherwise impair accuracy of the system.

Referring now particularly to Fig. 1, there is shown a transformer having a core 1 generally rectangular in shape, and which preferably, although not necessarily, has a laminated structure. The primary wlndmg comprises the coils 2, 2 wh1ch are arranged symmetrically, both with respect to posltlon and the number of ampere turns, on the two opposite legs of the core, as are also the secondary coils 3, 3. I I

The core structure and windings are symmetrically arranged on either side of a plane of symmetry, indicated by the broken llIle A-A, passing midway between the axes of the windings and parallel thereto, the plane being perpendicular to an imaginary plane (parallel to the plane of the paper, as vlewe'd in Fig. 1) passingthrough the axes of the windings. The core structure and windings are also symmetrical about a secondplane of symmetry, indicated by the broken line B 43, passing midway between the ends of the windings on each leg of the core, perpendicular to the axes of the windings and to the first plane A-A. Generally speaking, such a symmetrical arrangement results in the balancing out of the effects of any stray magnetic field or fields coming in, for example, from the front, side, or top of the core structure, as indicated by the arrows in Fig. 1a, but this is true only for a uniform field and a perfect balance of the core .and windings. In practice, however, the disturbing field is seldom uniform, due either to its nature or proximity, and it is diflicult to obtain the necessary accurate balance of. the core and windings.

In order to reduce the effect of any transformer unbalance and lack of field uniformity, the core structure is enclosed in one or more magnetic shields 4 symmetrically disposed about the planes of symmetry A A and B-B. Preferably, the spacing of the front and back, as at e, e, or f, f in Fig. 2 is also equal, although stray fields from this direction do not have the disturbing effect of a field from the other two directions.

The material of the shields preferably comprises a metal which has low reluctance, such as wrought iron, and therefore serves to shield from both electric and magnetic effects. The use of additional shields, as in Fig. 3, materially increases the gain in freedom from pick-up of stray fields, and by annealing the shields a further and larger gain is obtained. The core and windings may be spaced by sup ports of non-magnetizable material within the enclosing shield, and the shields may be separated from each other, in any suitable manner, not shown.

It is not essential that the portions of the shield adjacent the top or bottom of the core structure be equally spaced at all points from the top and bottom, respectively, or from the plane B-B, since they may be tapered, curved or have other contours, as long as the portions at the respective ends of'the core are symmetrically disposed on either side of the planes AA, and B--B. If the shield is not symmetrical, however, with respect to the planes of symmetry A-A, and BB, the advantage of the balance of the core and windings is negatived or lost. This is because an unsymmetrical shield may yield an unsymmetrical field inside, even though exposed to a uniform field outside.

Due to the symmetricalarrangement of the shield or shields in the manner aforesaid, the over-all dimensions of the transformer including the shield structure may be made apreci'ably smaller for a required freedom rom pick-up, or it will give a greater freedom from pick-up for a given size of transformer.

and shield than is possible with a simple shielded transformer, in which the core,

windings and shield, are not symmetrical in the manner described. Also, the shield or shields do not require radial symmetry about an axis of. the core structure, as, for example, in the case of toroidal coils with radially symmetrical shields, since the shields do not have to assume a particular configuration to conform to that of the core. The core may be ofthe rectangular type built up from standard punchings or laminations, or it may have any other desired configuratiom'or' it may be irregular in outline. The coils may be wound on bobbins and then placed over the legs of the core, and the transformer may thus be assembled or built up from stock parts, as in the usual transformer construction.

What I claim is:

1. A shielded transformer comprising a rectangular core structure having two parallel leg portions with the transformer windings symmetrically disposed thereon, said 'core structure and windings being symmetrically disposed on either side of two planes, one of which is midway between and parallel to the axes of the windings, and the other of' which passes through and midway between the ends of the windings, said planes being perpendicular to each other and to an imaginary plane through said axes.

2. A shielded transformer comprising core structure having two parallel leg portions with the transformer windings symmetrically disposed thereon, said core structure and windings being symmetrically disposed on either side of two planes, one of which is midway between and parallel to the axes of the windings, and the other of which passes through and midway between the ends of the windings, said planes being perpendicular to an imaginary plane through said axes, and a magnetic shield enclosing said core structure and windings and symmetrically disposed on either side of said planes of symmetry.

3. A shielded transformer comprising core structure having two parallel leg portions with the transformer windings symmetrically disposed thereon, said core structure and windings being symmetrically disposed on shields being symmetrically isposed on either' side of said planes of symmetry.

4. A shielded transformer comprising core structure having two parallel leg portions with the transformer windings symmetrically disposed thereon, said core structure and windings being symmetrically disposed on either side of two planes, one of which is midway between and parallel to the axes of the windings, and the other of which passes through and midway between the ends of the windings, said planes being perpendicular to an imaginary plane through said axes, and a casing enclosing said core structure and windings and comprising a metal of low reluctance, said casing being symmetrically disposed on either side of said planes of symmetry.

5. A shielded transformer comprising core structure having two parallel leg portions with the transformer windings symmetrically disposed thereon, said core structure and windings being symmetrically disposed on either side of two planes, one of which is midway between and parallel to the axes of the windings, and the other of which passes through and midwa between the ends of the windings, said p anes being perpendicular to an imaginary plane through said axes,-

a .first casing enclosing said core structure and windings, and a second casing enclosing the first named casing, said casings comprising a metal of low reluctance and being symmetrically disposed on either side of said planes of symmetry.

6. A shielded transformer comprising a rectangular core structure having parallel leg portions with the transformer windings symmetrically disposed on two of the parallel legs, the said legs and windings being symmetrically disposed on either side of two planes, one of which is midway between and parallel to the axes of the windings, and the other of which passes through and midway between the ends of the windings, said planes being perpendicular to an imaginary plane through said axes, and a magnetic shield enclosing said core structure and windings and symmetrically disposed on either side of said planes of symmetry.

7. A shielded transformer comprising a rectangular core structure having parallel leg portions with the transformer windings symmetrically disposed on two of the parallel legs, the said legs and windings being symmetrically disposed on either side of two planes, one of which is midway between and parallel to the axes of the windings, and the other of which passes through and midway between the ends of the windings. said planes being perpendicular to an imaginary plane through said axes. and a magnetic shield onclosing said core structure and windings and symmetrically disposed on either side of said planes of symmetry, said shield being composed of an annealed metal of high magnetic permeability.

8. A shielded transformer comprising a rectangular core structure having parallel leg portions, the primary and secondary windings of the transformer each comprising series-connected coils symmetrically wound on two of said parallel legs, said core structure and coils being symmetrically disposed on either side of two planes, one of which is midway between and parallel to the axes of the coils, and the other of which passes through and midway between the ends of thewindings, said planes being perpendicular to an imaginary plane through said axes, and a magnetic shield enclosing said core structure and coils and symmetrically disposed upon either side of said planes of symmetry.

ALBERT J. WILLIAMS, JR. 

